The embodiments described herein relate to vulcanized oil and water swellable particulate composite compositions, which may be used to form self-sealing cement slurries.
Subterranean formation operations (e.g., stimulation operations, sand control operations, completion operations, etc.) often involve placing a cement column around a casing (or liner) string in a wellbore. The cement column is formed by pumping a cement slurry through the bottom of the casing and out through an annulus between the outer casing wall and the formation face of the wellbore, known as primary cementing. The cement slurry cures in the annular space, thereby forming a column of hardened cement (or “sheath”) that, inter alia, supports and positions the casing in the wellbore and bonds the exterior surface of the casing to the subterranean formation. Among other things, the cement column may keep fresh water zones from becoming contaminated with produced fluids from within the wellbore. As used herein, the term “fluid” refers to liquid phase fluids and gas phase fluids. The cement column may also prevent unstable formations from caving in, thereby reducing the chance of a stuck drill pipe or a casing collapse. Additionally, the cement column may form a solid barrier to prevent fluid loss or contamination of production zones. Subsequent secondary cementing operations may also be performed.
The degree of success of a wellbore operation involving placement of a cement column therefore depends, at least in part, upon the successful cementing of the wellbore casing. During the completion and/or productive phase of a wellbore, for example, a cement sheath may be subjected to certain stresses including, among other things, pressure and temperature changes in the wellbore. Additionally, the cement sheath may shrink and create microannuli between the casing and cement and/or the formation and the cement sheath. As a result, the cement sheath may develop cracks internally or debond from the casing or subterranean formation itself, resulting in the formation of channels within the cement sheath or at its interfaces within the formation or the casing, thereby creating flow pathways for unwanted fluid invasion and migration. As used herein, the term “microannulus” and all of its variations refers to an inherent quality of cement, where the cement does not fully occupy the annulus between the casing and the formation face due to cement shrinkage. As used herein, the term “channel” refers to a defect in the matrix of the set cement, wherein the matrix of the set cement contains one or more cracks which may have sufficient inter-crack connectivity to provide continuous flow paths to enable undesirable fluid flow from the formation or other parts of the wellbore to the wellhead and/or wellbore. Such channels may result in hazardous situations (e.g., natural gas contamination or accumulation due to loss of zonal isolation).
The formation of channels in a cement sheath may result in loss of integrity of the cement sheath and failure of zonal isolation or wellbore structural failure. Because of the damaging effects of fluid invasion into a cement column, it is desirable to repair cracked or shrunken sheaths as they occur. Traditional techniques may involve, for example, squeeze cementing. As used herein, the term “squeeze cementing” refers to the process of forcing a cement slurry though channels, holes, or splits in a casing or liner so as to fill the voids and form an impenetrable barrier. Squeeze cementing can be particularly costly and may also result in a substantial reduction in production efficiency due to required downtime. Another technique may involve placing a water swellable compound (e.g., a polymer) into a cement slurry prior to pumping the cement slurry into a subterranean formation and forming a cement sheath. Traditional water swellable compounds when included in cement slurries may absorb water from the slurry during placement and increase the viscosity of a cement slurry so as to render it unpumpable and/or unsuitable for forming a stable cement sheath. Additionally, such water swellable compounds do not swell in the presence of non-aqueous fluids.